Carriages propelled by motors are widely used in various applications. Not only manned controlled carriages but also unmanned carriages such as Rail Guided Vehicles (RGVs) and Automatic Guided Vehicles (AGVs) are known. Outputs of motors in these carriages are transmitted to wheels via reducers and the carriages travel.
For example, Japanese Utility Model Application Publication No. Sho 62-59348 (“the '348 Publication”) discloses a driving device for wheels using a planetary gear mechanism. In this driving device, a speed reducer is provided in the wheel to downsize and simplify the device. Japanese Utility Model Application Publication No. Hei 1-65969 (“the '969 Publication”) discloses a special planetary gear reducer. In this reducer, a space for storing a pin for an external gear is reduced, and the speed reducer as a whole is downsized. Japanese Patent Application Publication No. 2000-233649 (“the '649 Publication”) discloses a driving wheel mechanism for an unmanned vehicle. With this driving wheel mechanism, drive wheels are reduced in size while ensuring sufficient load bearing performance, and the height and width of the unmanned vehicle are reduced.
In the above-described carriages, a wheel is attached to a turning portion of the reducer. In order to replace wheels of such a carriage, it was necessary to detach the entire drive unit that includes the wheels and the speed reducers from the carriage body, or to disassemble the speed reducer. Moreover, when replacing a brake unit of the carriage, it was necessary to detach the entire drive unit that includes the wheels and the speed reducers from the carriage body. Thus, removal and replacement of the wheels and the brake unit in the conventional carriages were extremely time consuming tasks.
For example, in the driving device described in the '348 Publication, an internal gear of the speed reducer and the like are disposed between an inner cover and an outer cover of a wheel. Accordingly, it is not possible for this driving device to remove only the wheel. To remove the wheel, it is necessary to disassemble the speed reducer. Moreover, to remove the wheel and a turning annulus (or a tire), it is necessary to remove a part or the whole of the frame that surrounds the wheel and the turning annulus. When a part or the whole of this frame is removed, a bearing provided on the outer side of the wheel (especially an outer cover) are exposed, which is not desirable. Furthermore, unless the bearing is removed, the wheel and the turning annulus cannot be removed.
As for the speed reducer described in the '969 Publication, since the turning portion (i.e., the case) of the reducer and the wheel are integrally formed, it is structurally impossible to separate only the wheel from the reducer. Even if the tire can be separated from the wheel, in order to remove the tire, it is necessary to further remove a housing and a side plate that surround the tire. However, since components of the reducer such as pins are supported by the side plate, it is structurally inevitable that the reducer is disassembled when the side plate is removed. It is not practical to replace only the tire while the wheel is attached to the carriage body. The tire is usually removed together with the wheel to replace the tire.
As for the mechanism described in the '649 Publication, a disk-shaped transmission plate is attached to an output portion of the reducer with a bolt, a wheel is attached to the outer peripheral edge of the transmission plate by bolts, and a holder ring is attached to the wheel. Therefore, in order to detach the wheel, these bolts have to be removed to detach the transmission plate and separate the wheel from the holder ring, which is time-consuming and troublesome. Moreover, when the wheel is removed, the bearing provided between a main bracket and the wheel is exposed, which is undesirable. Further, in the mechanism of The '649 Publication, since the transmission plate is provided so as to cover the reducer on the outside of the carriage body and rotates together with the output portion of the reducer, it is impossible to attach a device such as a brake unit to the transmission plate, which is inconvenient.